Updated at 12:10 p.m. ET
Paris is largely shut down Saturday, as investigators work to identify those behind Friday night's coordinated terror attacks, which killed 129 people and wounded more than 350. The Eiffel Tower and other public gathering spaces are closed.
This morning, French President Francois Hollande accused the self-proclaimed Islamic State of staging the coordinated attacks, calling them an "act of war." Shortly after his remarks, the extremist group claimed responsibility.
In addition to French victims, those hit by the attack include Americans, Britons and Swedes, according to officials from those countries.
The U.S. government "is working closely with French authorities to identify American victims," says the State Department's deputy spokesman, Mark Toner.
"We are aware there are Americans among the injured, and are offering them the full range of consular assistance," Toner says, adding that the U.S. Embassy in Paris has been working around the clock.
Police say they've identified one of the attackers as a young Frenchman who was born near Paris and was known to the authorities because of his radical views, according to Le Parisien and other news outlets. Le Parisien adds that police also found two passports — one Syrian, one Egyptian — near the attackers.
Saturday afternoon, Belgian police conducted "multiple searches and arrests" related to a Belgian license plate on a car that was reportedly used in Friday night's attacks, according to Belgium's Justice Minister Koen Geens.
France's Hollande said the military will continue to patrol Paris' streets and provide security to residents. Interior Minister Bernard Cazeneuve says all personnel remain on high alert Saturday.
The attack has put security on high alert in many areas – particularly where air travel is involved. Britain's busy Gatwick airport was the scene of at least two police actions Saturday. A Frenchman is being questioned about "what appears to be a firearm," the BBC says. Earlier, a terminal at the airport was temporarily closed after a security alert over suspicious behavior.
At the Bataclan concert hall, where at least 80 people were killed by men firing automatic rifles, French authorities were working Saturday morning to remove and identify bodies.
Concertgoers described scenes of horror at the venue, TV channel France 24 reports:
"There was blood everywhere, corpses everywhere. We heard screaming. Everyone was trying to flee," said Pierre Janaszak, a radio presenter who attended the concert and hid with several others at the venue.
Relaying a description of that attack by a witness who was inside the music hall, NPR's Eleanor Beardsley says, "The gunmen shot into the crowd screaming 'Allahu Akbar.' The concert stopped and people lay on the ground and they continued to shoot them."
Eleanor adds that the authorities say eight of the assailants are dead.
Dozens of other people were shot on the sidewalks outside cafes and bars in a working-class part of central Paris.
While authorities said late Friday that they believed all of the attackers had been killed, they're encouraging Parisians to stay home. Nearly all city facilities and buildings are closed today. Sporting events are canceled, large stores are closed, and many subway stations are also shut down.
Bruce Hoffman, a national security expert at Georgetown University, told NPR's Kelly McEvers that the attacks were reminiscent of the 2008 attack in Mumbai, India, which left more than 250 dead.
Osama bin Laden urged al-Qaida fighters to stage such attacks in the West in 2010, Hoffman noted.
"They certainly weren't amateurs," Hoffman said of the gunmen in Friday's attacks. "They were battle-hardened and they knew what they were doing. They had tremendous discipline, that they could deploy and strike at exactly the same time."
Years after France (and many other nations in Western Europe) relaxed its border controls, those official restrictions and checks are now being revived, as the BBC reports:
"Border and customs officers will check people, baggage and vehicles entering and leaving France by road, train, sea or plane, said customs official Melanie Lacuire."